A mode of expressing dislike to a person, or sermon, practised at Oxford by the students, in scraping their feet against the ground during the preachment; frequently done to testify their disapprobation of a proctor who has been, as they think, too rigorous.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Scraper * ScratchNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes